Tunable lasers have been frequently used in the field of atomic spectroscopy, molecular spectroscopy, laser cooling, semiconductor quantum dot spectroscopy, and in the study of quantum information processing.
As such devices, large dye lasers, ti-sapphire lasers and the like have been commercially available by optical component manufacturers. Recently, more inexpensive and compact external cavity diode laser (ECDLs) have come onto the market. In the ECDLs, there are two types; the Littrow-type and the Littman-type.